1. Field Of The Invention
The present invention relates to a method of detecting rubbing (contact) between a rotating body and a stationary body and, more particularly, to a method of detecting rubbing between a rotating body of a rotary machine rotatively driven by a working fluid and a stationary member such as a stationary sealing member disposed around the rotary body to prevent leak of the working fluid through the gap between the rotating body and the stationary part of the rotary machine.
2. Description Of The Prior Art
In a rotary machine such as a steam turbine, it is essential to prevent the leak of the working fluid for a safe and efficient operation of the machine. In order to prevent this leak of the working fluid, a noncontact type sealing measure employing a comb-like sealing device has been adopted. In this type of sealing measure, the rate of leak of the working fluid is decreased as the gap between the comb-like sealing member and the rotor is reduced. For this reason, the gap between the rotor and the comb-like sealing member is preferably reduced.
In this type of sealing measure, however, it is often experienced that the rotor is slightly displaced relatively to the comb-like sealing member to make a contact with the latter, due to various reasons such as change of operating condition of the turbine during transient period such as acceleration. This state of contact between the rotor and the sealing member is generally referred to as "rubbing".
Similar problem is experienced also in case of an oil shield which is used in combination with a plain bearing and adapted for preventing oil from leaking to the outside.
The rubbing between the rotating and stationary members generates a heat in the area around the point of contact, due to the friction, particularly when the rotating member is being rotated at a high speed as is the case of a steam turbine. This heat undesirably deflects the rotor to cause an unbalance of gyrating mass of the shaft, resulting in so-called rubbing vibration.
This rubbing vibration in some cases leads to a divergent vibration of increased amplitude. It is therefore strictly required to detect rubbing between the stationary member and the rotating member at an early stage and to take a necessary countermeasure without delay. A typical countermeasure is, for example, to reduce the rate of acceleration or to stop to continue the changing of load or operating condition to make the operation steady.
Various methods have been proposed up to now for detecting rubbing between the rotary member and the stationary member, one of which employs a vibrometer attached to the portion where the generation of rubbing is expected to take place. This detecting method is to pick up the vibration generated in the stationary member as a result of rubbing. This method, however, involves a problem that it is extremely difficult to discriminate the vibration caused by rubbing from the vibration caused by the machine itself. More specifically, the vibration detected by the vibrometer usually includes various components such as a component attributable to the resonance frequency of the stationary member itself, a component attributable to a change in the condition of the steam and so forth. It is possible only through operator's feeling and experience to judge whether the vibration component due to rubbing is involved by the vibration as detected by the vibrometer. Such a judgement based upon the operator's feeling and experience is not reliable and, therefore, is defective.
In order to obviate the above stated problem, it has been proposed in Japanese Patent Laid-open Publication No. 80874/1975 to compare the actually measured vibration pattern with previously memorized patterns of vibrations attributable to various reasons. According to this method, the cause of the vibration is detected as a disposal instruction corresponding to a cause such as rubbing is selected in accordance with the result of the pattern recognition or comparison.
This method relying upon the comparison of patterns making use of a pattern recognition technique, however, poses a new problem that the extent of overlap or coincidence of two patterns, with which it is judged that the cause of the vibration, e.g. rubbing, is taking place, can hardly be determined definitely. A fluctuation of detecting precision is therefore unavoidable.
At the same time, the above-mentioned Japanese Patent Laid-open Publication No. 80874/1975 offers only how to discriminate the causes of the vibration, and fails to teach how to range the position at which the cause of the vibration is taking place.